Topic: Late April Astronomy Bulletin

[Clive]

SOLAR VARIABILITY LINKED TO LA NINA EVENTS
National Center for Atmospheric Research/University Corporation for Atmospheric Research

A new study shows a correlation between the end of solar cycles and a switch from El Nino to La Nina conditions in the Pacific Ocean, suggesting that solar variability can drive seasonal weather variability on Earth. If the connection holds up, it could significantly improve the predictability of the largest El Nino and La Nina events, which have a number of seasonal climate effects over land. For example, the southern United States tends to be warmer and drier during a La Nina, while the northern U.S. tends to be colder and wetter. The appearance (and disappearance) of spots on the Sun -- the outwardly visible signs of solar variability -- have been observed by humans for hundreds of years. The waxing and waning of the number of sunspots takes place over approximately 11-year cycles, but these cycles do not have distinct beginnings and endings. This fuzziness in the length of any particular cycle has made it challenging for scientists to match up the 11-year cycle with changes happening on Earth. In the new study, the researchers rely on a more precise 22-year "clock" for solar activity derived from the Sun's magnetic polarity cycle, which they outlined as a more regular alternative to the 11-year solar cycle in several companion studies published recently in peer-reviewed journals. The 22-year cycle begins when oppositely charged magnetic bands that wrap the Sun appear near the star's polar latitudes, according to their recent studies. Over the cycle, these bands migrate toward the equator -- causing sunspots to appear as they travel across the mid-latitudes. The cycle ends when the bands meet in the middle, mutually annihilating one another in what the research team calls a terminator event.  These terminators provide precise guideposts for the end of one cycle and the beginning of the next.

The researchers imposed these terminator events over sea surface temperatures in the tropical Pacific stretching back to 1960. They found that the five terminator events that occurred between that time and November 2010 all coincided with a flip from an El Nino (when sea surface temperatures are warmer than average) to a La Nina (when the sea surface temperatures are cooler than average). The end of the most recent solar cycle -- which is unfolding now -- is also coinciding with the beginning of a La Nina event. In fact, the researchers did a number of statistical analyses to determine the likelihood that the correlation was just a fluke. They found there was only a 1 in 5,000 chance or less (depending on the statistical test) that all five terminator events included in the study would randomly coincide with the flip in ocean temperatures. Now that a sixth terminator event -- and the corresponding start of a new solar cycle in 2020 -- has also coincided with an La Nina event, the chance of a random occurrence is even more remote, the authors said. The paper does not delve into what physical connection between the Sun and Earth could be responsible for the correlation, but the authors note that there are several possibilities that warrant further study, including the influence of the Sun's magnetic field on the amount of cosmic rays that escape into the solar system and ultimately bombard Earth. However, a robust physical link between cosmic rays variations and climate has yet to be determined. If further research can establish that there is a physical connection and that changes on the Sun are truly causing variability in the oceans, then we may be able to improve our ability to predict El Nino and La Nina events.


5,000 TONS OF EXTRATERRESTRIAL DUST FALL TO EARTH ANNUALLY
CNRS

Every year, our planet encounters dust from comets and asteroids. These interplanetary dust particles pass through our atmosphere and give rise to shooting stars. Some of them reach the ground in the form of micrometeorites. An international program conducted for nearly 20 years has determined that 5,200 tons per year of these micrometeorites reach the ground. Micrometeorites have always fallen on our planet. These interplanetary dust particles from comets or asteroids are particles of a few tenths to hundredths of a millimetre that have passed through the atmosphere and reached the Earth's surface. To collect and analyse these micrometeorites, six expeditions have taken place over the last two decades in the heart of Antarctica. It is an ideal collection spot due to the low accumulation rate of snow and the near absence of terrestrial dust. These expeditions have collected enough extraterrestrial particles (ranging from 30 to 200 micrometres in size), to measure their annual flux, which corresponds to the mass accreted on Earth per square metre per year. If these results are applied to the whole planet, the total annual flux of micrometeorites represents 5,200 tons per year. This is the main source of extraterrestrial matter on our planet, far ahead of larger objects such as meteorites, for which the flux is less than ten tons per year. A comparison of the flux of micrometeorites with theoretical predictions confirms that most micrometeorites probably come from comets (80%) and the rest from asteroids. This is valuable information to better understand the role played by these interplanetary dust particles in supplying water and carbonaceous molecules on the young Earth.


ODYSSEY ORBITER MAPS MARS FOR 20 YEARS
NASA

For two decades, the longest-lived spacecraft at the Red Planet has helped locate water ice, assess landing sites, and study the planet’s mysterious moons. NASA’s 2001 Mars Odyssey spacecraft launched 20 years ago on April 7, making it the oldest spacecraft still working at the Red Planet. The orbiter, which takes its name from Arthur C. Clarke’s classic sci-fi novel “2001: A Space Odyssey” (Clarke blessed its use before launch), was sent to map the composition of the Martian surface, providing a window to the past so scientists could piece together how the planet evolved. But it’s done far more than that, uncovering troves of water ice, serving as a crucial communications link for other spacecraft, and helping to pave the way not just for safer landings but also future astronauts. Look at almost any mapping study of the Martian surface, and it probably includes Odyssey data. For many years, the most complete global maps of Mars were made using Odyssey’s infrared camera, called the Thermal Emission Imaging System, or THEMIS. The camera measures the surface temperature day and night, allowing scientists to determine what physical materials, such as rock, sand, or dust, exist. Its data reveals the presence of these materials based on how they heat up or cool down over the course of a Martian day. The net effect of two decades’ worth of all that mapping? Scientists haven’t just used the data to map valley networks and craters, they’ve also been able to spot sandstone, iron-rich rocks, salts, and more – findings that help lend deeper insight to Mars’ story. THEMIS has sent back more than 1 million images since it began circling Mars. The images and maps it’s produced highlight the presence of hazards, such as topographic features and boulders, but they also help ensure the safety of future astronauts by showing the location of resources such as water ice. This aids the Mars science community and NASA in deciding where to send landers and rovers – including the Perseverance rover, which touched down on Feb. 18, 2021.

From early on, Odyssey has served as a long-distance call centre for NASA’s rovers and landers, sending their data back to Earth as part of the Mars Relay Network. The idea of Mars relay goes back to the 1970’s, when the two Viking landers sent science data and images through an orbiter back to Earth. An orbiter can carry radios or antennas capable of sending back more data than a surface spacecraft. But Odyssey made the process routine when it began conveying data to and from NASA’s Spirit and Opportunity rovers. Each day, the rovers could go somewhere new and send fresh images back to Earth. Through a relay like Odyssey, scientists got more data sooner, while the public got more Mars images to be excited over. Odyssey has supported over 18,000 relay sessions. These days, it shares the communications task with NASA’s Mars Reconnaissance Orbiter and MAVEN, along with the ESA (European Space Agency) Trace Gas Orbiter. Odyssey has done such a thorough job of studying the Martian surface that scientists have started turning its THEMIS camera to capture unique views of Mars’ moons Phobos and Deimos. As with the Martian surface, studying each moon’s thermophysics helps scientists determine the properties of materials on their surfaces. Such information can offer glimmers into their past: It’s unclear whether the moons are captured asteroids or chunks of Mars, blasted off the surface by an ancient impact. Future missions, like the Japanese Space Agency’s Martian Moons eXploration (MMX) spacecraft, will seek to land on these moons. In the distant future, missions might even create bases on them for astronauts. And if they do, they’ll rely on data from an orbiter that began its odyssey at the start of the millennium.


X-RAYS DETECTED FROM URANUS
Harvard-Smithsonian Center for Astrophysics

Astronomers have detected X-rays from Uranus for the first time, using NASA's Chandra X-ray Observatory. This result may help scientists learn more about this enigmatic ice giant planet in our solar system. Uranus is the seventh planet from the Sun and has two sets of rings around its equator. The planet, which has four times the diameter of Earth, rotates on its side, making it different from all other planets in the solar system. Since Voyager 2 was the only spacecraft to ever fly by Uranus, astronomers currently rely on telescopes much closer to Earth, like Chandra and the Hubble Space Telescope, to learn about this distant and cold planet that is made up almost entirely of hydrogen and helium. In the new study, researchers used Chandra observations taken in Uranus in 2002 and then again in 2017. They saw a clear detection of X-rays from the first observation, just analyzed recently, and a possible flare of X-rays in those obtained fifteen years later. What could cause Uranus to emit X-rays? The answer: mainly the Sun. Astronomers have observed that both Jupiter and Saturn scatter X-ray light given off by the Sun, similar to how Earth's atmosphere scatters the Sun's light. While the authors of the new Uranus study initially expected that most of the X-rays detected would also be from scattering, there are tantalizing hints that at least one other source of X-rays is present. If further observations confirm this, it could have intriguing implications for understanding Uranus. One possibility is that the rings of Uranus are producing X-rays themselves, which is the case for Saturn's rings. Uranus is surrounded by charged particles such as electrons and protons in its nearby space environment. If these energetic particles collide with the rings, they could cause the rings to glow in X-rays. Another possibility is that at least some of the X-rays come from auroras on Uranus, a phenomenon that has previously been observed on this planet at other wavelengths.

On Earth, we can see colourful light shows in the sky called auroras, which happen when high-energy particles interact with the atmosphere. X-rays are emitted in Earth's auroras, produced by energetic electrons after they travel down the planet's magnetic field lines to its poles and are slowed down by the atmosphere. Jupiter has auroras, too. The X-rays from auroras on Jupiter come from two sources: electrons traveling down magnetic field lines, as on Earth, and positively charged atoms and molecules raining down at Jupiter's polar regions. However, scientists are less certain about what causes auroras on Uranus. Chandra's observations may help figure out this mystery. Uranus is an especially interesting target for X-ray observations because of the unusual orientations of its spin axis and its magnetic field. While the rotation and magnetic field axes of the other planets of the solar system are almost perpendicular to the plane of their orbit, the rotation axis of Uranus is nearly parallel to its path around the Sun. Furthermore, while Uranus is tilted on its side, its magnetic field is tilted by a different amount, and offset from the planet's centre. This may cause its auroras to be unusually complex and variable. Determining the sources of the X-rays from Uranus could help astronomers better understand how more exotic objects in space, such as growing black holes and neutron stars, emit X-rays.


TRIO OF FAST-SPINNING BROWN DWARFS MAY REVEAL ROTATIONAL SPEED LIMIT
ESO

Brown dwarfs, sometimes known as “failed stars,” can spin at upwards of 200,000 mph, but there may be a limit to how fast they can go. Using data from NASA’s Spitzer Space Telescope, scientists have identified the three fastest-spinning brown dwarfs ever found. More massive than most planets but not quite heavy enough to ignite like stars, brown dwarfs are cosmic in-betweeners. And though they aren’t as well-known as stars and planets to most people, they are thought to number in the billions in our galaxy. In a new study, astronomers argue that these three rapid rotators could be approaching a spin speed limit for all brown dwarfs, beyond which they would break apart. The rapidly rotating brown dwarfs are all about the same diameter as Jupiter but between 40 and 70 times more massive. They each rotate about once per hour, while the next-fastest known brown dwarfs rotate about once every 1.4 hours and Jupiter spins once every 10 hours. Based on their size, that means the largest of the three brown dwarfs whips around at more than 360,000 kilometres per hour). Brown dwarfs, like stars or planets, are already spinning when they form. As they cool down and contract, they spin faster, just like when a spinning ice skater draws her arms into her body. Scientists have measured the spin rates of about 80 brown dwarfs, and they vary from less than two hours (including the three new entries) to tens of hours. With so much variety among the brown dwarf speeds already measured, it surprised the authors of the new study that the three fastest brown dwarfs ever found have almost the exact same spin rate (about one full rotation per hour) as each other. This cannot be attributed to the brown dwarfs having formed together or being at the same stage in their development, because they are physically different: One is a warm brown dwarf, one is cold, and the other falls between them. Since brown dwarfs cool as they age, the temperature differences suggest these brown dwarfs are different ages.

The authors aren’t chalking this up to coincidence. They think the members of the speedy trio have all reached a spin speed limit, beyond which a brown dwarf could break apart. All rotating objects generate centripetal force, which increases the faster the object spins. On a carnival ride, this force can threaten to throw riders from their seats; in stars and planets, it can tear the object apart. Before a spinning object breaks apart, it will often start bulging around its midsection as it deforms under the pressure. Scientists call this oblation. Saturn, which rotates once every 10 hours like Jupiter, has a perceptible oblation. Based on the known characteristics of the brown dwarfs, they likely have similar degrees of oblation, according to the paper authors. Considering that brown dwarfs tend to speed up as they age, are these objects regularly exceeding their spin speed limit and being torn apart? In other rotating cosmic objects, like stars, there are there natural braking mechanisms that stop them from destroying themselves. It’s not clear yet if similar mechanisms exist in brown dwarfs. The maximum spin rate of any object is determined not only by its total mass but by how that mass is distributed. That’s why, when very rapid spin rates are involved, understanding a brown dwarf’s interior structure becomes increasingly important: The material inside likely shifts and deforms in ways that could change how fast the object can spin. Similar to gas planets such as Jupiter and Saturn, brown dwarfs are composed mostly of hydrogen and helium. But they are also significantly denser than most giant planets. Scientists think the hydrogen in the core of a brown dwarf is under such tremendous pressures that it starts behaving like a metal rather than an inert gas: It has free-floating conducting electrons, much like a copper conductor. That changes how heat is conducted through the interior and with very fast spin rates, may also affect how the mass inside an astronomical object is distributed. Physicists use observations, laboratory data, and mathematics to create models of what brown dwarf interiors should look like and how they should behave, even under extreme conditions. But current models show that the maximum brown dwarf spin speed should be about 50% to 80% faster than the one-hour rotation period described in the new study. It is possible that these theories don’t have the full picture yet. Some unappreciated factor may be coming into play that doesn’t let the brown dwarf spin faster. Additional observations and theoretical work may yet reveal whether there’s some braking mechanism that stops brown dwarfs from self-destruction and whether there are brown dwarfs spinning even faster in the darkness.


DOUBLE QUASARS IN MERGING GALAXIES
NASA/Goddard Space Flight Center

Hubble astronomers found a pair of quasars that are so close to each other they look like a single object in ground-based telescopic photos. The researchers believe the quasars are very close to each other because they reside in the cores of two merging galaxies. A quasar is a brilliant beacon of intense light from the centre of a distant galaxy that can outshine the entire galaxy. It is powered by a supermassive black hole voraciously feeding on inflating matter, unleashing a torrent of radiation. It is estimated that in the distant Universe, for every 1,000 quasars, there is one double quasar. Quasars are scattered all across the sky and were most abundant 10 billion years ago. There were a lot of galaxy mergers back then feeding the black holes. Therefore, astronomers theorize there should have been many dual quasars during that time. The observations are important because a quasar's role in galactic encounters plays a critical part in galaxy formation, the researchers say. As two close galaxies begin to distort each other gravitationally, their interaction funnels material into their respective black holes, igniting their quasars. Over time, radiation from these high-intensity "light bulbs" launch powerful galactic winds, which sweep out most of the gas from the merging galaxies. Deprived of gas, star formation ceases, and the galaxies evolve into elliptical galaxies. Astronomers have discovered more than 100 double quasars in merging galaxies so far. However, none of them is as old as the two double quasars in this study. The Hubble images show that quasars within each pair are only about 10,000 light-years apart. By comparison, our Sun is 26,000 light-years from the supermassive black hole in the centre of our galaxy. The pairs of host galaxies will eventually merge, and then the quasars also will coalesce, resulting in an even more massive, single solitary black hole.

Astronomers first needed to figure out where to point Hubble to study them. The challenge is that the sky is blanketed with a tapestry of ancient quasars that flared to life 10 billion years ago, only a tiny fraction of which are dual. It took an imaginative and innovative technique that required the help of the European Space Agency's Gaia satellite and the ground-based Sloan Digital Sky Survey to compile a group of potential candidates for Hubble to observe. The researchers then enlisted the Gaia observatory to help pinpoint potential double-quasar candidates. Gaia measures the positions, distances, and motions of nearby celestial objects very precisely. But the team devised a new, innovative application for Gaia that could be used for exploring the distant Universe. They used the observatory's database to search for quasars that mimic the apparent motion of nearby stars. The quasars appear as single objects in the Gaia data. However, Gaia can pick up a subtle, unexpected "jiggle" in the apparent position of some of the quasars it observes. The quasars aren't moving through space in any measurable way, but instead their jiggle could be evidence of random fluctuations of light as each member of the quasar pair varies in brightness. Quasars flicker in brightness on timescales of days to months, depending on their black hole's feeding schedule. This alternating brightness between the quasar pair is similar to seeing a railroad crossing signal from a distance. As the lights on both sides of the stationary signal alternately flash, the sign gives the illusion of "jiggling." When the first four targets were observed with Hubble, it revealed that two of the targets are two close pairs of quasars. Although the team is convinced of their result, they say there is a slight chance that the Hubble snapshots captured double images of the same quasar, an illusion caused by gravitational lensing. This phenomenon occurs when the gravity of a massive foreground galaxy splits and amplifies the light from the background quasar into two mirror images. However, the researchers think this scenario is highly unlikely because Hubble did not detect any foreground galaxies near the two quasar pairs. Galactic mergers were more plentiful billions of years ago, but a few are still happening today. One example is NGC 6240, a nearby system of merging galaxies that has two and possibly even three supermassive black holes. An even closer galactic merger will occur in a few billion years when our Milky Way galaxy collides with neighbouring Andromeda galaxy. The galactic tussle would likely feed the supermassive black holes in the core of each galaxy, igniting them as quasars.


CARBON’S INTERSTELLAR JOURNEY TO EARTH
University of Michigan

We are made of stardust, the saying goes, and a pair of studies finds that may be more true than we previously thought. The first study finds that most of the carbon on Earth was likely delivered from the interstellar medium, the material that exists in space between stars in a galaxy. This likely happened well after the protoplanetary disk, the cloud of dust and gas that circled our young Sun and contained the building blocks of the planets, formed and warmed up. Carbon was also likely sequestered into solids within one million years of the Sun's birth -- which means that carbon, the backbone of life on Earth, survived an interstellar journey to our planet.

Previously, researchers thought carbon in the Earth came from molecules that were initially present in nebular gas, which then accreted into a rocky planet when the gases were cool enough for the molecules to precipitate. Astronomers point out in this study that the gas molecules that carry carbon wouldn't be available to build the Earth because once carbon vaporizes, it does not condense back into a solid. Much of carbon was delivered to the disk in the form of organic molecules. Because of this, the team inferred most of Earth's carbon was likely inherited directly from the interstellar medium, avoiding vaporization entirely. To better understand how Earth acquired its carbon, astronomers estimated the maximum amount of carbon Earth could contain. To do this, they compared how quickly a seismic wave travels through the core to the known sound velocities of the core. This told the researchers that carbon likely makes up less than half a percent of Earth's mass. Understanding the upper bounds of how much carbon the Earth might contain tells the researchers information about when the carbon might have been delivered here. A planet's carbon must exist in the right proportion to support life as we know it. Too much carbon, and the Earth's atmosphere would be like Venus, trapping heat from the Sun and maintaining a temperature of about 880 degrees Fahrenheit. Too little carbon, and Earth would resemble Mars: an inhospitable place unable to support water-based life, with temperatures around minus 60.

In a second study by the same group of authors looked at how carbon is processed when the small precursors of planets, known as planetesimals, retain carbon during their early formation. By examining the metallic cores of these bodies, now preserved as iron meteorites, they found that during this key step of planetary origin, much of the carbon must be lost as the planetesimals melt, form cores and lose gas. This upends previous thinking. Most models have the carbon and other life-essential materials such as water and nitrogen going from the nebula into primitive rocky bodies, and these are then delivered to growing planets such as Earth or Mars. But this skips a key step, in which the planetesimals lose much of their carbon before they accrete to the planets. The two studies both describe two different aspects of carbon loss -- and suggest that carbon loss appears to be a central aspect in constructing the Earth as a habitable planet. Answering whether or not Earth-like planets exist elsewhere can only be achieved by working at the intersection of disciplines like astronomy and geochemistry. Over the history of our galaxy alone, rocky planets like the Earth or a bit larger have been assembled hundreds of millions of times around stars like the Sun. Can we extend this work to examine carbon loss in planetary systems more broadly? Such research will take a diverse community of scholars.


DOUBT CAST OVER 70% OF UNIVERSE COMPOSITION :
University of Copenhagen - Faculty of Science

Until now, researchers have believed that dark energy accounted for nearly 70 percent of the ever-accelerating, expanding Universe. For many years, this mechanism has been associated with the so-called cosmological constant, developed by Einstein in 1917, that refers to an unknown repellent cosmic power. But because the cosmological constant -- known as dark energy -- cannot be measured directly, numerous researchers, including Einstein, have doubted its existence -- without being able to suggest a viable alternative. In a new study a model was tested that replaces dark energy with a dark matter in the form of magnetic forces. The usual understanding of how the Universe's energy is distributed is that it consists of five percent normal matter, 25 percent dark matter and 70 percent dark energy. In the new model, the 25 percent share of dark matter is accorded special qualities that make the 70 percent of dark energy redundant. We don't know much about dark matter other than that it is a heavy and slow particle. But then researchers wondered -- what if dark matter had some quality that was analogous to magnetism in it? We know that as normal particles move around, they create magnetism. And, magnets attract or repel other magnets -- so what if that's what's going on in the Universe? That this constant expansion of dark matter is occurring thanks to some sort of magnetic force?

The question served as the foundation for the new computer model, where researchers included everything that they know about the Universe -- including gravity, the speed of the Universe's expansion and X, the unknown force that expands the Universe. They developed a model that worked from the assumption that dark matter particles have a type of magnetic force and investigated what effect this force would have on the Universe. It turns out that it would have exactly the same effect on the speed of the Universe's expansion as we know from dark energy. However, there remains much about this mechanism that has yet to be understood by the researchers. And it all needs to be checked in better models that take more factors into consideration. The team says the discovery may just be a coincidence. But if it isn't, it is truly incredible. It would change our understanding of the universe's composition and why it is expanding. As far as our current knowledge, our ideas about dark matter with a type of magnetic force and the idea about dark energy are equally wild. Only more detailed observations will determine which of these models is the more realistic.